Periplasmic Zinc Management and Homeostasis in Paracoccus denitrificans

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ABSTRACT The prevalence of antibiotic resistance among pathogenic bacteria has become a major health concern and has spurred the search for novel antibiotic targets. A particularly promising target is the superfamily of bacterial ATP-binding cassette (ABC) transporters, which couple the hydrolysis of ATP to the transport of a wide variety of solutes across the cell membrane. Bacterial ABC transporters work in conjunction with a high affinity solute binding protein (SBP) that specifically binds substrate and delivers it to the transporter. In Salmonella enterica and Streptococcus pneumoniae among others, disruption of genes encoding ABC transporters and SBPs specific for Zn dramatically attenuates virulence in animal models, highlighting these systems as potent drug targets. We have identified two Zn-specific ABC transporter operons in Paracoccus denitrificans, ZnuABC and AztABCD, and have characterized a hitherto hypothetical protein (AztD) that acts as a Zn chaperone, directly transferring Zn to the SBP of that system (AztC). This project will utilize P. dentrificans as a model for highly homologous systems in human pathogens belonging to the carbapenem-resistant Enterobacteriacaea (CRE). These organisms are associated with broad- spectrum antimicrobial resistance and are the causative agents of potentially deadly nosocomial infections. We will determine the precise mechanism of metal binding and transfer for AztC and AztD proteins from P. denitrificans and the CRE pathogen Citrobacter koseri using structural and biophysical techniques. The physiological roles of the Azt and Znu systems will be determined by making genetic knockouts of these genes in P. denitrficans and characterizing growth deficient phenotypes in Zn-limited medium. High-resolution structural information combined with in vivo functionality will yield new insight into the mechanisms of transition metal import in bacteria and potentially provide a basis for the rational design of metal uptake inhibitors as antibiotics for multi- drug resistant pathogens. !